Imaging lens

ABSTRACT

An imaging lens includes a first lens having positive refractive power; a second lens having positive refractive power; a third lens; a fourth lens; a fifth lens; and a sixth lens having negative refractive power, arranged in this order from an object side to an image plane side. The sixth lens is formed in a shape so that a curvature radius of a surface thereof on the object side and a curvature radius of a surface thereof on the image plane side are negative. The surface of the sixth lens on the image plane side has the specific curvature radius so that a specific conditional expression is satisfied.

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT

The present invention relates to an imaging lens for forming an image ofan object on an imaging element such as a CCD sensor and a CMOS sensor.In particular, the present invention relates to an imaging lens suitablefor mounting in a relatively small camera such as a camera to be builtin a cellular phone, a portable information terminal, or the like, adigital still camera, a security camera, a vehicle onboard camera, and anetwork camera.

In these years, in place of cellular phones that are intended mainly formaking phone calls, so-called “smartphones”, i.e., multifunctionalcellular phones which can run various application software as well as avoice call function, have been more widely used. When applicationsoftware is run on smartphones, it is possible to perform functions suchas those of digital still cameras and car navigation systems on thesmartphones. In order to perform those various functions, most models ofsmartphones include cameras.

Generally speaking, product groups of such smartphones are oftencomposed according to specifications for beginners to advanced users.Among them, an imaging lens to be mounted in a product designed for theadvanced users is required to have a high-resolution lens configurationso as to be also applicable to a high pixel count imaging element ofthese years, as well as a small size.

As a method of attaining the high-resolution imaging lens, there hasbeen a method of increasing the number of lenses that compose theimaging lens. However, the increase of the number of lenses easilycauses an increase in the size of the imaging lens. Therefore, the lensconfiguration having a large number of lenses has a disadvantage interms of mounting in a small-sized camera such as the above-describedsmartphones. Accordingly, in development of the imaging lens, it hasbeen necessary to attain high resolution of the imaging lens, whilelimiting the number of lenses that composes the imaging lens.

In recent years, with advancement of technology to attain a high pixelcount of an imaging element, technology for manufacturing lenses hasbeen also dramatically advanced. Therefore, it is achievable to producea smaller sized imaging lens which is equivalent to a conventionalimaging lens in terms of the number of lenses. On the other hand, insome cases, high optical performance of the imaging lens has beendiscussed in terms of the number of lenses that compose the imaginglens. Due to limitation on a space inside a camera to mount the imaginglens, while downsizing of the imaging lens is still important, it isgetting even more important to achieve high resolution of the imaginglens.

In case of a lens configuration composed of six lenses, due to the largenumber of lenses of the imaging lens, it has high flexibility in design.In addition, it has potential to attain satisfactory correction ofaberrations and downsizing of the imaging lens in a balanced manner,which is necessary for high-resolution imaging lenses. For example,Patent Reference has disclosed an imaging lens with the six-lensconfiguration as the conventional imaging lens.

Patent Reference: Japanese Patent Application Publication No.2013-195587

The imaging lens described in Patent Reference includes a first lensthat is positive and directs a convex surface thereof to an object side;a second lens that is negative and directs a concave surface thereof toan image plane side, a third lens that is negative and directs a concavesurface thereof to the object side, a fourth and fifth lenses that arepositive and direct convex surfaces thereof to the image plane side, anda sixth lens that is negative and directs a concave surface thereof tothe object side. According to the conventional imaging lens disclosed inPatent Reference, by satisfying conditional expressions of a ratiobetween a focal length of the first lens and a focal length of the thirdlens and a ratio between a focal length of the second lens and a focallength of the whole lens system, it is achievable to satisfactorilycorrect a distortion and a chromatic aberration.

Each year, functions and sizes of cellular phones and smartphones aregetting higher and smaller, and the level of a small size required foran imaging lens is even higher than before. In case of the imaging lensdisclosed in Patent Reference, since a distance from an object-sidesurface of the first lens to an image plane of an imaging element islong, there is a limit to achieve satisfactory correction of aberrationswhile further downsizing the imaging lens to satisfy the above-describeddemands.

Alternatively, there is another method to reduce the level of downsizingrequired for the imaging lens by providing a camera as a separate unitfrom cellular phones or smartphones. However, in terms of convenience orportability, cellular phones or smartphones with built-in cameras arestill dominantly preferred. Therefore, there remains a demand for smallimaging lenses with high resolution.

Such a problem is not specific to the imaging lens to be mounted incellular phones and smartphones. Rather, it is a common problem even foran imaging lens to be mounted in a relatively small camera such asdigital still cameras, portable information terminals, security cameras,vehicle onboard cameras, and network cameras.

In view of the above-described problems in conventional techniques, anobject of the present invention is to provide an imaging lens that canattain both downsizing thereof and satisfactory aberration correction.

Further objects and advantages of the present invention will be apparentfrom the following description of the invention.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, in order to attainthe objects described above, there is provided an imaging lens thatforms an image of an object on an imaging element. The imaging lens ofthe invention includes a first lens having positive refractive power; asecond lens having positive refractive power; a third lens; a fourthlens; a fifth lens; and a sixth lens having negative refractive power,arranged in the order from an object side to an image plane side.According to the first aspect of the invention, the sixth lens is formedin a shape so as to have negative curvature radii both on theobject-side surface thereof and image plane-side surface thereof. Whenthe whole lens system has the focal length f and a curvature radius ofthe image plane-side surface of the sixth lens is R6r, the imaging lensof the invention satisfies the following conditional expression (1):

−10’R6r/f<−1   (1)

According to the imaging lens of the invention, it is achievable tosuitably downsize the imaging lens with the first and the second lenses,which have positive refractive powers. In addition, when the imaginglens satisfies the conditional expression (1), it is also achievable tosatisfactorily correct aberrations. When the imaging lens satisfies theconditional expression (1), it is achievable to satisfactorily correctastigmatism and a distortion. In addition, when the imaging lenssatisfies the conditional expression (1), it is also achievable torestrain an incident angle of a light beam emitted from the imaging lensto an imaging element within the range of a chief ray angle (CRA). As iswell known, a so-called chief ray angle (CRA) is set in advance for animaging element, i.e. a range of an incident angle of a light beam thatcan be taken in the image plane.

When a light beam outside the range of CRA enters the imaging element,“shading” occurs, which is an obstacle for achieving satisfactoryimage-forming performance. When the value exceeds the upper limit of −1in the conditional expression (1), at periphery of the image, theastigmatic difference increases and the distortion increases in apositive direction (image plane side). Therefore, it is difficult toobtain satisfactory image-forming performance. Moreover, the incidentangle of a light beam emitted from the imaging lens to the image planeis large, so that it is difficult to restrain the incident angle withinthe range of CRA. On the other hand, when the value is below the lowerlimit of −10, it is advantageous for correction of the astigmatism.However, since the distortion increases in a negative direction (objectside) at periphery of the image, it is difficult to obtain satisfactoryimage-forming performance. Moreover, the incident angle of a light beamemitted from the imaging lens is small, so that it is difficult torestrain the incident angle within the range of CRA.

According to a second aspect of the invention, when a curvature radiusof the object-side surface of the fourth lens is R4f and a curvatureradius of the image plane-side surface of the fourth lens is R4r, theimaging lens having the above-described configuration preferablysatisfies the following conditional expression (2):

0.5<|R4f/R4r|<2.0   (2)

When the imaging lens satisfies the conditional expression (2), it isachievable to restrain the field curvature, the chromatic aberration ofmagnification, and the astigmatism within satisfactory ranges in abalanced manner. When the value exceeds the upper limit of 2.0, theimage-forming surface curves to the object side, and the field curvatureis insufficiently corrected. In addition, the chromatic aberration ofmagnification is excessively corrected (an image-forming point at ashort wavelength moves in a direction to be away from the optical axisrelative to that at a reference wavelength). Therefore, it is difficultto obtain satisfactory image-forming performance. On the other hand,when the value is below the lower limit of 0.5, it is advantageous forcorrection of the chromatic aberration of magnification. However, theimage-forming surface tilts to the image plane side, the field curvatureis excessively corrected, and the astigmatic difference increases.Therefore, it is difficult to obtain satisfactory image-formingperformance.

According to a third aspect of the invention, when the second lens has afocal length f2 and the third lens has a focal length f3, the imaginglens having the above-described configuration preferably satisfies thefollowing conditional expression (3):

0.2<|f3/f2|<1.2   (3)

When the imaging lens satisfies the conditional expression (3), it isachievable to satisfactorily correct the chromatic aberration and theastigmatism. When the value exceeds the upper limit of 1.2, it isadvantageous for correction of the chromatic aberration of magnificationfor an off-axis light flux. However, the axial chromatic aberration isinsufficiently corrected (a focal position at a short wavelength movesto the object side relative to that at a reference wavelength).Moreover, in the astigmatism, a sagittal image surface curves to theobject side and the astigmatic difference increases. Therefore, it isdifficult to obtain satisfactory image-forming performance. On the otherhand, when the value is below the lower limit of 0.2, it is advantageousfor correction of the axial chromatic aberration. However, the chromaticaberration of magnification for the off-axis light flux is excessivelycorrected. Moreover, the astigmatism increases, so that it is difficultto obtain satisfactory image-forming performance.

According to a fourth aspect of the invention, when the whole lenssystem has a focal length f and the third lens has a focal length f3,the imaging lens having the above-described configuration preferablysatisfies the following conditional expression (4):

−2.0<f3/f<−0.5   (4)

When the imaging lens satisfies the conditional expression (4), it isachievable to satisfactorily correct the chromatic aberration and thespherical aberration. When the value exceeds the upper limit of −0.5, itis advantageous for correction of the axial chromatic aberration.However, the chromatic aberration of magnification for the off-axislight flux is excessively corrected, and the spherical aberrationincreases in the positive direction and is excessively corrected. Forthis reason, it is difficult to obtain satisfactory image-formingperformance. On the other hand, when the value is below the lower limitof −2.0, it is advantageous for correction of the chromatic aberrationof magnification for the off-axis light flux. However, the axialchromatic aberration is insufficiently corrected. In addition, thespherical aberration increases in the negative direction and isinsufficiently corrected. Therefore, it is difficult to obtainsatisfactory image-forming performance.

According to a fifth aspect of the invention, when the third lens has afocal length f3 and the sixth lens has a focal length f6, the imaginglens having the above-described configuration preferably satisfies thefollowing conditional expression (5):

0.5<f3/f6<1.5   (5)

When the imaging lens satisfies the conditional expression (5), it ispossible to restrain the chromatic aberration, the distortion, and thespherical aberration respectively within satisfactory ranges in abalanced manner. When the value exceeds the upper limit of 1.5, it isadvantageous for correction of the distortion and the chromaticaberration of magnification. However, the axial chromatic aberration isinsufficiently corrected, and the spherical aberration is insufficientlycorrected. Therefore, it is difficult to obtain satisfactoryimage-forming performance. On the other hand, when the value is belowthe lower limit of 0.5, it is advantageous for correction of the axialchromatic aberration. However, the distortion increases in the positivedirection and the spherical aberration is excessively corrected. Inaddition, the chromatic aberration of magnification for the off-axislight flux is excessively corrected. Therefore, it is difficult toobtain satisfactory image-forming performance.

According to a sixth aspect of the invention, when the whole lens systemhas the focal length f and the sixth lens has a focal length f6, theimaging lens having the above-described configuration preferablysatisfies the following conditional expression (6):

−2.0<f6/f<−0.5   (6)

When the imaging lens satisfies the conditional expression (6), it isachievable to satisfactorily correct the chromatic aberration ofmagnification, the astigmatism, and the distortion, while downsizing theimaging lens. When the value exceeds the upper limit of −0.5, it isadvantageous for downsizing of the imaging lens. However, the chromaticaberration of magnification is excessively corrected. Therefore, it isdifficult to obtain satisfactory image-forming performance. Moreover,the incident angle of a light beam emitted from the imaging lens islarge, and it is difficult to restrain the incident angle within therange of CRA. On the other hand, when the value is below the lower limitof −2.0, it is advantageous for correction of chromatic aberration ofmagnification for the off-axis light flux. However, it is difficult todownsize the imaging lens. Moreover, in the astigmatism, the tangentialimage surface curves to the image plane side and the astigmaticdifference increases. Therefore, it is difficult to obtain satisfactoryimage-forming performance.

According to a seventh aspect of the invention, when the whole lenssystem has the focal length f and a distance along the optical axisbetween the third lens and the fourth lens is D34, the imaging lenshaving the above-described configuration preferably satisfies thefollowing conditional expression (7):

0.05<D34/f<0.2   (7)

When the imaging lens satisfies the conditional expression (7), it isachievable to restrain the distortion, the astigmatism, the fieldcurvature, and the chromatic aberration of magnification respectivelywithin satisfactory ranges in a balanced manner. When the value exceedsthe upper limit of 0.2, the distortion increases in the positivedirection, and the field curvature is excessively corrected. Moreover,the astigmatic difference increases, and the chromatic aberration ofmagnification for the off-axis light flux is excessively corrected. Forthis reason, it is difficult to obtain satisfactory image-formingperformance. When the value is below the lower limit of 0.05, thedistortion increases in the negative direction, and the field curvatureis insufficiently corrected. Moreover, the astigmatic differenceincreases and the spherical aberration is excessively corrected.Therefore, it is difficult to obtain satisfactory image-formingperformance.

According to an eighth aspect of the invention, when the whole lenssystem has the focal length f and a distance along the optical axisbetween the fourth lens and the fifth lens is D45, the imaging lenshaving the above-described configuration preferably satisfies thefollowing conditional expression (8):

0.02<D45/f<0.2   (8)

When the imaging lens satisfies the conditional expression (8), it isachievable to satisfactorily correct the distortion, the astigmatism,the spherical aberration, and the chromatic aberration of magnification.When the value exceeds the upper limit of 0.2, both the sphericalaberration and the field curvature are insufficiently corrected, and theastigmatic difference increases. Moreover, the distortion increases in anegative direction and the chromatic aberration of magnification for theoff-axis light flux is excessively corrected. Therefore, it is difficultto obtain satisfactory image-forming performance. On the other hand,when the value is below the lower limit of 0.02, it is advantageous forcorrection of the distortion. However, both the spherical aberration andthe field curvature are excessively corrected, and the astigmaticdifference increases. Therefore, it is difficult to obtain satisfactoryimage-forming performance.

According to a ninth aspect of the invention, when the whole lens systemhas the focal length f and a distance along the optical axis between thefifth lens and the sixth lens is D56, the imaging lens having theabove-described configuration preferably satisfies the followingconditional expression (9):

0.05<D56/f<0.2   (9)

When the imaging lens satisfies the conditional expression (9), it isachievable to restrain the distortion, the astigmatism, and thechromatic aberration of magnification respectively within satisfactoryranges in a balanced manner, while restraining the incident angle of alight beam emitted from the imaging lens within the range of CRA. Whenthe value exceeds the upper limit of 0.2, it is easy to restrain theincident angle within the range of CRA. However, in the astigmatism, thesagittal image surface tilts to the image plane side, so that anastigmatic difference increases. Therefore, it is difficult to obtainsatisfactory image-forming performance. On the other hand, when thevalue is below the lower limit of 0.05, the distortion increases in thepositive direction, and the chromatic aberration of magnification forthe off-axis light flux is excessively corrected. Moreover, in theastigmatism, the sagittal image surface tilts to the object side and theastigmatic difference increases. Therefore, it is difficult to obtainsatisfactory image-forming performance.

According to a tenth aspect of the invention, when the fifth lens has athickness T5 along the optical axis and the sixth lens has a thicknessT6 along the optical axis, the imaging lens having the above-describedconfiguration preferably satisfies the following conditional expression(10):

0.5<T5/T6<3.0   (10)

When the imaging lens satisfies the conditional expression (10), it isachievable to satisfactorily correct the field curvature and theastigmatism. When the value exceeds the upper limit of 3.0, the fieldcurvature is excessively corrected. In addition, in the astigmatism, thesagittal image surface tilts to the image plane side, and the astigmaticdifference increases. For this reason, it is difficult to obtainsatisfactory image-forming performance. On the other hand, when thevalue is below the lower limit of 0.5, the field curvature isinsufficiently corrected and the astigmatism increases. Therefore, it isdifficult to obtain satisfactory image-forming performance.

According to a eleventh aspect of the invention, when the whole lenssystem has a focal length f, a composite focal length of the fifth lensand the sixth lens is f56, the imaging lens having the above-describedconfiguration preferably satisfies the following conditional expression(11):

−10<f56/f<−0.5   (11)

When the imaging lens satisfies the conditional expression (11), it isachievable to restrain the chromatic aberration, the astigmatism, andthe distortion respectively within satisfactory ranges in a balancedmanner. When the value exceeds the upper limit of −0.5, it isadvantageous for correction of the chromatic aberration ofmagnification. However, the axial chromatic aberration is insufficientlycorrected. Moreover, in the astigmatism, the tangential image surfacetilts to the object side and the astigmatic difference increases.Therefore, it is difficult to obtain satisfactory image-formingperformance. On the other hand, when the value is below the lower limitof −10, it is advantageous for correction of the axial chromaticaberration. However, in the astigmatism, the tangential image surfacetilts to the image plane side and the astigmatic difference increases.Further, the spherical aberration is excessively corrected, and it isdifficult to obtain satisfactory image-forming performance.

According to a twelfth aspect of the invention, when the first lens hasAbbe's number vd1, the second lens has Abbe's number vd2, and the thirdlens has Abbe's number vd3, in order to satisfactorily correct thechromatic aberration, the imaging lens preferably satisfies thefollowing conditional expressions (12) through (14):

35<vd1<75   (12)

35 <vd2<75   (13)

15<vd3<35   (14)

According to a thirteenth aspect of the invention, when the fourth lenshas Abbe's number vd4, the fifth lens has Abbe's number vd5, and thesixth lens has Abbe's number vb6, in order to more satisfactorilycorrect the chromatic aberration, the imaging lens preferably satisfiesthe following conditional expressions (15) through (17):

15<vd4<35   (15)

35<vd5<75   (16)

35 <vd6<75   (17)

In the imaging lens having the above-described configuration, the sixthlens preferably has the image plane-side surface formed in an asphericsurface, so that a curvature thereof increases monotonously away from anoptical axis thereof toward a periphery thereof in a directionperpendicular to the optical axis.

As described above, in case of an imaging element, CRA is set inadvance. Therefore, in order to obtain satisfactory image-formingperformance, it is necessary to restrain the incident angle of a lightbeam emitted from the imaging lens to the image plane within the rangeof CRA. In order to attain further downsizing of the imaging lens, theemitting angle of a light beam emitted from the image plane-side surfaceof the sixth lens is large near periphery of the lens. Therefore, it isdifficult to restrain the incident angle to the image plane within therange of CRA over the whole image.

On this point, in case of the sixth lens of the invention, the imageplane-side surface thereof is formed as an aspheric shape, in which acurvature thereof increases as it goes to the periphery of the lens,i.e., formed in a shape such that a curvature thereof is large near thelens periphery. Therefore, it is achievable to keep the emitting angleof a light beam from the lens periphery small, and it is achievable tosuitably restrain the incident angle to the image plane within the rangeof CRA over the whole image.

Here, according to the invention, as described above, the shape of thelens is specified by the positive/negative sign of the curvature radius.Whether the curvature radius of the lens is positive or negative isdetermined based on general definition. More specifically, taking atraveling direction of light as positive, if a center of a curvatureradius is on the image plane side when viewed from a lens surface, thecurvature radius is positive. If a center of a curvature radius is onthe object side, the curvature radius is negative.

Therefore, “an object side surface, a curvature radius of which ispositive” means the object side surface is a convex surface. “An objectside surface, a curvature radius of which is negative” means the objectside surface is a concave surface. “An image plane side surface, acurvature radius of which is positive” means the image plane sidesurface is a concave surface. “An image plane side surface, a curvatureradius of which is negative” means the image plane side surface is aconvex surface. Here, a curvature radius used herein refers to aparaxial curvature radius, and may not fit to general shapes of thelenses in their sectional views all the time.

According to the imaging lens of the present invention, it is possibleto provide a small-sized imaging lens that is especially suitable formounting in a small-sized camera, while having high resolution withsatisfactory correction of aberrations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a sectional view of a schematic configuration of an imaginglens in Numerical Data Example 1 of the present invention;

FIG. 2 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 1;

FIG. 3 is an aberration diagram showing a spherical aberration,astigmatism, and a distortion of the imaging lens of FIG. 1;

FIG. 4 shows a sectional view of a schematic configuration of an imaginglens in Numerical Data Example 2 of the present invention;

FIG. 5 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 4;

FIG. 6 is an aberration diagram showing a spherical aberration,astigmatism, and a distortion of the imaging lens of FIG. 4;

FIG. 7 shows a sectional view of a schematic configuration of an imaginglens in Numerical Data Example 3 of the present invention;

FIG. 8 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 7;

FIG. 9 is an aberration diagram showing a spherical aberration,astigmatism, and a distortion of the imaging lens of FIG. 7;

FIG. 10 shows a sectional view of a schematic configuration of animaging lens in Numerical Data Example 4 of the present invention;

FIG. 11 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 10;

FIG. 12 is an aberration diagram showing a spherical aberration,astigmatism, and a distortion of the imaging lens of FIG. 10;

FIG. 13 shows a sectional view of a schematic configuration of animaging lens in Numerical Data Example 5 of the present invention;

FIG. 14 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 13;

FIG. 15 is an aberration diagram showing a spherical aberration,astigmatism, and a distortion of the imaging lens of FIG. 13;

FIG. 16 shows a sectional view of a schematic configuration of animaging lens in Numerical Data Example 6 of the present invention;

FIG. 17 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 16;

FIG. 18 is an aberration diagram showing a spherical aberration,astigmatism, and a distortion of the imaging lens of FIG. 16;

FIG. 19 shows a sectional view of a schematic configuration of animaging lens in Numerical Data Example 7 of the present invention;

FIG. 20 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 19; and

FIG. 21 is an aberration diagram showing a spherical aberration,astigmatism, and a distortion of the imaging lens of FIG. 19.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereunder, referring to the accompanying drawings, an embodiment of thepresent invention will be fully described.

FIGS. 1, 4, 7, 10, 13, 16, and 19 are schematic sectional views of theimaging lenses in Numerical Data Examples 1 to 7 according to theembodiment, respectively. Since the imaging lenses in those NumericalData Examples have the same basic configuration, the lens configurationof the embodiment will be described with reference to the illustrativesectional view of Numerical Data Example 1.

As shown in FIG. 1, according to the embodiment, the imaging lensincludes a first lens L1 having positive refractive power, a second lensL2 having positive refractive power, a third lens L3, a fourth lens L4,a fifth lens L5, and a sixth lens L6 having negative refractive power,arranged in the order from an object side to an image plane side.Between the sixth lens L6 and an image plane IM of an imaging element,there is provided a filter 10. The filter 10 is omissible.

The first lens L1 is formed in a shape such that a curvature radius r1of an object-side surface thereof and a curvature radius r2 of an imageplane-side surface thereof are both positive, so as to have a shape of ameniscus lens directing a convex surface thereof on an object side nearan optical axis X. The shape of the first lens L1 is not limited to theone in Numerical Data Example 1, and can be varied. Numerical DataExamples 3 and 6 are examples, in which the first lens L1 is formed in ashape, such that a curvature radius r2 of an image plane-side surfacethereof is negative, i.e., so as to have a shape of a biconvex lens nearan optical axis X. In addition to the above-described shape, the firstlens L1 also can be formed in a shape, such that the curvature radius r1is infinite and the curvature radius r2 is negative, so as to have ashape of a plano-convex lens directing a flat surface to the object sidenear the optical axis X.

Alternatively, the first lens L1 also can be formed in a shape, suchthat both the curvature radius r1 and the curvature radius r2 arenegative, so as to have a shape of a meniscus lens directing a concavesurface to the object side near the optical axis X.

In the imaging lens of the embodiment, there is provided an aperturestop ST between the first lens L1 and the second lens L2. When theaperture stop ST is provided in such position, the presence of theimaging lens in a camera is emphasized. Therefore, it is possible toappeal to users by the luxurious impression, high lens performance, etc.as a part of design of the camera. Here, the position of the aperturestop ST may not be limited to the one described in Numerical DataExample 1. For example, in order to easily assemble the imaging lens,the aperture stop ST may be provided on the object side of the firstlens L1.

The second lens L2 is formed in a shape such that a curvature radius r3of an object-side surface thereof is positive and a curvature radius r4of an image plane-side surface thereof is negative, so as to have ashape of a biconvex lens near the optical axis X. The shape of thesecond lens L2 may not be limited to the one in Numerical DataExample 1. The imaging lens of Numerical Data Examples 2, 3, 4, 6, and 7are examples, in which the second lens L2 is formed in a shape such thata curvature radius r3 and a curvature radius r4 are both negative, so asto have a shape of a meniscus lens directing a concave surface thereofto the object side near the optical axis X. On the other hand, theimaging lens of Numerical Data Example 5 is an example, in which thesecond lens L2 is formed in a shape such that the curvature radius r3and the curvature radius r4 are both positive, so as to have a shape ofa meniscus lens directing a convex surface thereof to the object sidenear the optical axis X.

The third lens L3 has negative refractive power. In addition, the thirdlens L3 is formed in a shape such that a curvature radius r5 of anobject-side surface thereof and a curvature radius r6 of an imageplane-side surface thereof are both positive, so as to have a shape of ameniscus lens directing a convex surface thereof to the object side nearthe optical axis X. The shape of the third lens L3 is not limited to theone in Numerical Data Example 1. However, the third lens L3 ispreferably formed such that the curvature radius r6 of the image planeside-side surface thereof is positive. The imaging lens of NumericalData Example 3 is an example, in which the third lens L3 is formed in ashape such that the curvature radius r5 is negative and the curvatureradius r6 is positive, so as to have a shape of a biconcave lens nearthe optical axis X.

The fourth lens L4 has positive refractive power. In addition, thefourth lens L4 is formed in a shape such that a curvature radius r7 ofan object-side surface thereof and a curvature radius r8 of an imageplane-side surface thereof are both negative, so as to have a shape of ameniscus lens directing a concave surface thereof to the object sidenear the optical axis X. The refractive power of the fourth lens L4 isnot limited to positive ones. Numerical Data Examples 4 and 5 areexamples, in which the refractive power of the fourth lens L4 isnegative. Moreover, the shape of the fourth lens L4 is also not limitedto the one in Numerical Data Example 1. The imaging lens of NumericalData Example 2 is an example, in which the fourth lens L4 is formed in ashape such that the curvature radius r7 is positive and the curvatureradius r8 is negative, so as to have a shape of a biconvex lens near theoptical axis X.

On the other hand, the imaging lens of Numerical Data Example 4 is anexample, in which the fourth lens L4 is formed in a shape such that thecurvature radius r7 and the curvature radius r8 are both positive, so asto have a shape of a meniscus lens directing a convex surface thereof tothe object side near the optical axis X. The fourth lens L4 can be alsoformed in a shape such that the curvature radius r7 and the curvatureradius r8 are both infinite and has refractive power near the lensperiphery.

The fifth lens L5 has positive refractive power. In addition, the fifthlens L5 is formed in a shape such that a curvature radius r9 of anobject-side surface thereof and a curvature radius r10 of an imageplane-side surface thereof are both positive, so as to have a shape of ameniscus lens directing a convex surface thereof to the object side nearthe optical axis X. The refractive power of the fifth lens L5 is notlimited to positive ones. Numerical Data Examples 6 and 7 are examples,in which the refractive power of the fifth lens L5 is negative.

The shape of the fifth lens L5 is not limited to the one in NumericalData Example 1. The fifth lens L5 can be formed in any shape, as long asit is a shape of a meniscus lens. The imaging lens of Numerical DataExample 7 is an example, in which the fifth lens L5 is formed in a shapesuch that the curvature radius r9 and the curvature radius r10 are bothnegative, so as to have a shape of a meniscus lens directing a concavesurface thereof to the object side near the optical axis X. The fifthlens L5 can be also formed in a shape such that the curvature radius r9and the curvature radius r10 are both infinite and has refractive powernear the lens periphery.

The sixth lens L6 is formed in a shape such that a curvature radius r11of an object-side surface thereof and a curvature radius r12 of an imageplane-side surface thereof are both negative, so as to have a shape of ameniscus lens directing a concave surface thereof to the object sidenear the optical axis X. In the sixth lens L6, the image plane-sidesurface thereof is formed as an aspheric shape not having an inflexionpoint. More specifically, the image plane-side surface of the sixth lensL6 is formed as an aspheric shape, such that the curvature monotonouslyincreases as the distance from the optical axis in a directionperpendicular to the optical axis X is longer.

The image plane-side surface of the fifth lens L5 and the object-sidesurface of the sixth lens L6 are formed as aspheric shapes havinginflexion points. With those shapes of the fifth lens L5 and the sixthlens L6, it is achievable to satisfactorily correct the off-axischromatic aberration of magnification as well as the axial chromaticaberration. In addition, it is also achievable to suitably restrain anincident angle of a light beam emitted from the imaging lens to theimage plane IM within the range of CRA.

According to the embodiment, the imaging lens satisfies the followingconditional expressions (1) to (11):

−10<R6r/f<−1   (1)

0.5<|R4f/R4r1<2.0   (2)

0.2<If3/f2|<1.2   (3)

−2.0<f3/f<−0.5   (4)

0.5<f3/f6<1.5   (5)

−2.0<f6/f<−0.5   (6)

0.05<D34/f<0.2   (7)

0.02<D45/f<0.2   (8)

0.05<D56/f<0.2   (9)

0.5<T5/T6<3.0   (10)

−10<f56/f<−0.5   (11)

In the above conditional expressions:

-   f: Focal length of a whole lens system-   f2: Focal length of the second lens L2-   f3: Focal length of the third lens L3-   f6: Focal length of the sixth lens L6-   f56: Composite focal length of the fifth lens L5 and the sixth lens    L6-   R4f: Curvature radius of an object-side surface of a fourth lens L4    (=r7)-   R4r: Curvature radius of an image plane-side surface of the fourth    lens L4 (=r8)-   R6r: Curvature radius of an image plane-side surface of the sixth    lens L6 (=r12)-   D34: Distance along the optical axis X between the third lens L3 and    the fourth lens L4-   D45: Distance along the optical axis X between the fourth lens L4    and the fifth lens L5-   D56: Distance along the optical axis X between the fifth lens L5 and    the sixth lens L6-   T5: Thickness of the fifth lens L5 on the optical axis-   T6: Thickness of the sixth lens L6 along the optical axis

In addition, the imaging lens according to the embodiment furthersatisfies the following conditional expressions (12) through (17):

35<vd1<75   (12)

35<vd2<75   (13)

15<vd3<35   (14)

15<vd4<35   (15)

35<vd5<75   (16)

35<vd6<75   (17)

In the above conditional expressions:

-   vd1: Abbe's number of the first lens L1-   vd2: Abbe's number of the second lens L2-   vd3: Abbe's number of the third lens L3-   vd4: Abbe's number of the fourth lens L4-   vd5: Abbe's number of the fifth lens L5-   vd6: Abbe's number of the sixth lens L6

Here, it is not necessary to satisfy all of the conditional expressions,and it is achievable to obtain an effect corresponding to the respectiveconditional expression when any single one of the conditionalexpressions is individually satisfied.

In the embodiment, all lens surfaces are formed as an aspheric surface.The aspheric shapes of the lens surfaces are expressed by the followingformula:

$Z = {\frac{C \cdot H^{2}}{1 + \sqrt{1 - {( {1 + k} ) \cdot C^{2} \cdot H^{2}}}} + {\sum( {{An} \cdot H^{n}} )}}$

In the above conditional expressions:

-   Z: Distance in a direction of the optical axis-   H: Distance from the optical axis in a direction perpendicular to    the optical axis-   C: Paraxial curvature (=1/r, r: paraxial curvature radius)-   k: Conic constant-   An: The nth order aspheric coefficient

Next, Numerical Data Examples of the imaging lens of the embodiment willbe described. In each Numerical Data Example, f represents a focallength of the whole lens system, Fno represents an F-number, and ωrepresents a half angle of view, respectively. In addition, i representsa surface number counted from the object side, r represents a curvatureradius, d represents a distance on the optical axis between lenssurfaces (surface spacing), nd represents a refractive index, and vdrepresents an Abbe's number, respectively. Here, aspheric surfaces areindicated with surface numbers i affixed with * (asterisk).

Numerical Data Example 1 Basic Lens Data

TABLE 1 f = 5.00 mm Fno = 1.97 ω = 35.0° i r d nd νd [mm] ∞ ∞ L1  1*2.172 0.507 1.5348 55.7 f1 = 4.439  2*(ST) 23.418 0.088 L2  3* 62.0590.930 1.5348 55.7 f2 = 7.188  4* −4.077 0.030 L3  5* 13.009 0.185 1.650321.5 f3 = −5.353  6* 2.731 0.519 (=D34) L4  7* −3.824 0.578 1.6142 25.6f4 = 31.940  8* −3.384 0.356 (=D45) L5  9* 2.440 0.636 1.5348 55.7 f5 =33.868 10* 2.564 0.537 (=D56) L6 11* −2.831 0.585 1.5348 55.7 f6 =−6.187 12* −21.039 0.100 13 ∞ 0.210 1.5168 64.2 14 ∞ 0.543 (IM) ∞

-   f56=−8.684 mm-   T5=0.636 mm-   T6=0.585 mm

TABLE 2 Aspherical surface data i k A4 A6 A8 A10 A12 A14 A16 1 0−2.865E−02 5.884E−03 −7.544E−02 1.114E−01 −1.201E−01 6.396E−02−1.280E−02 2 0 −2.211E−02 −2.310E−02 −8.985E−03 2.161E−02 −2.415E−021.504E−02 −3.777E−03 3 0 2.807E−02 −5.775E−03 1.103E−02 −1.337E−031.671E−02 −1.450E−02 3.161E−03 4 0 3.791E−02 −7.263E−02 8.920E−02−9.100E−02 5.844E−02 −1.912E−02 2.272E−03 5 0 −1.796E−01 5.171E−02−3.727E−02 4.113E−02 −1.528E−02 3.716E−03 −8.146E−04 6 0 −1.747E−019.424E−02 −5.710E−02 2.347E−02 3.570E−03 −6.929E−03 2.056E−03 7 03.260E−02 −7.024E−02 9.834E−02 −1.217E−01 6.509E−02 −1.853E−02 1.120E−038 0 −8.894E−02 8.145E−02 −4.299E−02 2.172E−03 8.205E−03 −5.473E−031.319E−03 9 0 −2.250E−01 9.241E−02 −4.747E−02 1.902E−02 −5.979E−038.511E−04 −1.171E−06 10 0 −1.417E−01 3.036E−02 −6.219E−03 3.649E−041.686E−04 −2.906E−05 9.905E−07 11 0 −2.327E−02 5.474E−03 6.025E−044.197E−06 −2.712E−05 2.340E−06 −2.280E−08 12 0 −2.773E−02 9.926E−03−1.636E−03 6.048E−05 9.800E−06 −1.086E−06 3.279E−08

The values of the respective conditional expressions are as follows:

-   R6r/f=−4.21-   |R4f/R4r|=1.13-   |f3/f2|=0.74-   f3/f=−1.07-   f3/f6=0.87-   f6/f=−1.24-   D34/f=0.10-   D45/f=0.07-   D56/f=0.11-   T5/T6=1.09-   f56/f=−1.74

Accordingly, the imaging lens of Numerical Data Example 1 satisfies theabove-described conditional expressions. The distance on the opticalaxis X from the object-side surface of the first lens L1 to the imageplane IM (air conversion length for the filter 10) is 5.732 mm, anddownsizing of the imaging lens is attained.

FIG. 2 shows a lateral aberration that corresponds to a ratio H of eachimage height to the maximum image height (hereinafter referred to as“image height ratio H”), which is divided into a tangential directionand a sagittal direction (The same is true for FIGS. 5, 8, 11, 14, 17,and 20). Furthermore, FIG. 3 shows a spherical aberration (mm),astigmatism (mm), and a distortion (%), respectively. In the astigmatismdiagram, an aberration on a sagittal image surface S and an aberrationon a tangential image surface T are respectively indicated (The same istrue for FIGS. 6, 9, 12, 15, 18, and 21). As shown in FIGS. 2 and 3,according to the imaging lens of Numerical Data Example 1, theaberrations are satisfactorily corrected.

Numerical Data Example 2 Basic Lens Data

TABLE 3 f = 5.07 mm Fno = 2.18 ω = 34.6° i r d nd νd [mm] ∞ ∞ L1  1*2.294 0.523 1.5348 55.7 f1 = 4.433  2*(ST) 65.389 0.168 L2  3* −7.2690.589 1.5348 55.7 f2 = 9.980  4* −3.165 0.043 L3  5* 12.655 0.282 1.650321.5 f3 = −6.382  6* 3.098 0.799 (=D34) L4  7* 89.212 0.381 1.6142 25.6f4 = 70.954  8* −85.067 0.377 (=D45) L5  9* 2.152 0.647 1.5348 55.7 f5 =17.156 10* 2.518 0.480 (=D56) L6 11* −2.909 0.605 1.5348 55.7 f6 =−6.435 12* −20.173 0.100 13 ∞ 0.210 1.5168 64.2 14 ∞ 0.600 (IM) ∞

-   f56=−12.969 mm-   T5=0.647 mm-   T6=0.605 mm

TABLE 4 Aspherical surface data i k A4 A6 A8 A10 A12 A14 A16 1 0−2.692E−02 9.316E−03 −8.017E−02 1.220E−01 −1.226E−01 6.307E−02−1.235E−02 2 0 −3.010E−02 −1.722E−02 −4.431E−03 2.087E−02 −2.030E−021.343E−02 −3.668E−03 3 0 3.456E−02 −1.087E−02 9.471E−03 1.704E−031.842E−02 −1.623E−02 3.470E−03 4 0 5.285E−02 −8.893E−02 1.021E−01−9.374E−02 5.507E−02 −1.598E−02 1.632E−03 5 0 −1.652E−01 5.051E−02−3.245E−02 3.253E−02 −1.103E−02 1.493E−03 −9.939E−05 6 0 −1.851E−011.116E−01 −7.913E−02 5.353E−02 −1.749E−02 7.893E−04 6.998E−04 7 0−1.136E−02 −3.660E−02 7.062E−02 −8.119E−02 3.936E−02 −9.096E−035.715E−04 8 0 −1.366E−01 1.250E−01 −7.186E−02 8.515E−03 9.790E−03−5.874E−03 1.091E−03 9 0 −2.500E−01 9.359E−02 −4.967E−02 2.134E−02−7.284E−03 1.113E−03 −5.552E−06 10 0 −1.484E−01 2.914E−02 −5.570E−033.415E−04 1.494E−04 −2.686E−05 9.678E−07 11 0 −2.392E−02 6.575E−031.564E−04 8.575E−05 −3.812E−05 3.225E−06 −4.240E−08 12 0 −2.156E−027.804E−03 −1.431E−03 6.737E−05 8.209E−06 −1.059E−06 3.564E−08

The values of the respective conditional expressions are as follows:

-   R6r/f=−3.98-   |R4f/R4r|=1.05-   |f3/f2|=0.64-   f3/f=−1.26-   f3/f6=0.99-   f6/f=−1.27-   D34/f=0.16-   D45/f=0.07-   D56/f=0.09-   T5/T6=1.07-   f56/f=−2.56

Accordingly, the imaging lens of Numerical Data Example 2 satisfies theabove-described conditional expressions. The distance on the opticalaxis X from the object-side surface of the first lens L1 to the imageplane IM (air conversion length for the filter 10) is 5.732 mm, anddownsizing of the imaging lens is attained.

FIG. 5 shows a lateral aberration that corresponds to the image heightratio H, and FIG. 6 shows a spherical aberration (mm), astigmatism (mm),and a distortion (%), respectively. As shown in FIGS. 5 and 6, accordingto the imaging lens of Numerical Data Example 2, the aberrations arealso satisfactorily corrected.

Numerical Data Example 3 Basic Lens Data

TABLE 5 f = 5.02 mm Fno = 1.97 ω = 34.9° i r d nd νd [mm] ∞ ∞ L1  1*2.238 0.543 1.5348 55.7 f1 = 4.018  2*(ST) −49.092 0.199 L2  3* −7.3630.648 1.5348 55.7 f2 = 8.825  4* −2.964 0.102 L3  5* −44.861 0.2411.6503 21.5 f3 = −5.153  6* 3.630 0.526 (=D34) L4  7* −4.221 0.5071.6142 25.6 f4 = 19.645  8* −3.270 0.360 (=D45) L5  9* 2.470 0.6321.5348 55.7 f5 = 40.930 10* 2.536 0.515 (=D56) L6 11* −2.872 0.6321.5348 55.7 f6 = −6.368 12* −19.750 0.100 13 ∞ 0.210 1.5168 64.2 14 ∞0.589 (IM) ∞

-   f56=−8.554 mm-   T5=0.632 mm-   T6=0.632 mm

TABLE 6 Aspherical surface data i k A4 A6 A8 A10 A12 A14 A16 1 0−2.872E−02 5.810E−03 −7.546E−02 1.114E−01 −1.197E−01 6.404E−02−1.292E−02 2 0 −2.332E−02 −1.970E−02 −8.639E−03 2.121E−02 −2.367E−021.550E−02 −4.017E−03 3 0 4.465E−02 −6.590E−03 1.054E−02 −1.721E−041.770E−02 −1.531E−02 3.327E−03 4 0 4.829E−02 −7.147E−02 8.883E−02−9.111E−02 5.869E−02 −1.865E−02 2.218E−03 5 0 −1.808E−01 4.898E−02−3.577E−02 4.245E−02 −1.596E−02 3.539E−03 −6.353E−04 6 0 −1.713E−019.174E−02 −5.773E−02 2.435E−02 3.641E−03 −7.007E−03 2.033E−03 7 03.805E−02 −6.926E−02 9.963E−02 −1.215E−01 6.509E−02 −1.810E−02 1.056E−038 0 −7.863E−02 8.382E−02 −4.335E−02 1.588E−03 8.100E−03 −5.489E−031.314E−03 9 0 −2.269E−01 9.307E−02 −4.732E−02 1.905E−02 −5.908E−038.398E−04 −4.881E−06 10 0 −1.460E−01 3.083E−02 −6.181E−03 3.532E−041.673E−04 −2.864E−05 9.672E−07 11 0 −2.305E−02 5.205E−03 6.072E−046.299E−06 −2.724E−05 2.324E−06 −1.965E−08 12 0 −2.737E−02 9.732E−03−1.593E−03 5.875E−05 9.749E−06 −1.080E−06 3.212E−08

The values of the respective conditional expressions are as follows:

-   R6r/f=−3.93-   |R4f/R4r|=1.29-   |f3/f2|=0.58-   f3/f=−1.03-   f3/f6=0.81-   f6/f=−1.27-   D34/f=0.10-   D45/f=0.07-   D56/f=0.10-   T5/T6=1.00-   f56/f=−1.70

Accordingly, the imaging lens of Numerical Data Example 3 satisfies theabove-described conditional expressions. The distance on the opticalaxis X from the object-side surface of the first lens L1 to the imageplane IM (air conversion length for the filter 10) is 5.732 mm, anddownsizing of the imaging lens is attained.

FIG. 8 shows a lateral aberration that corresponds to the image heightratio H, and FIG. 9 shows a spherical aberration (mm), astigmatism (mm),and a distortion (%), respectively. As shown in FIGS. 8 and 9, accordingto the imaging lens of Numerical Data Example 3, the aberrations arealso satisfactorily corrected.

Numerical Data Example 4 Basic Lens Data

TABLE 7 f = 5.13 mm Fno = 2.00 ω = 34.3° i r d nd νd [mm] ∞ ∞ L1  1*2.238 0.518 L5348 55.7 f1 = 4.367  2*(ST) 49.357 0.182 L2  3* −7.0100.597 1.5348 55.7 f2 = 10.087  4* −3.139 0.031 L3  5* 11.516 0.2731.6503 21.5 f3 = −6.710  6* 3.136 0.818 (=D34) L4  7* 47.016 0.3621.6142 25.6 f4 = −101.330  8* 26.705 0.372 (=D45) L5  9* 2.121 0.6591.5348 55.7 f5 = 15.810 10* 2.524 0.486 (=D56) L6 11* −2.912 0.6661.5348 55.7 f6 = −6.557 12* −18.541 0.100 13 ∞ 0.210 1.5168 64.2 14 ∞0.542 (IM) ∞

-   f56=−14.525mm-   T5=0.659mm-   T6=0.666mm

TABLE 8 Aspherical surface data i k A4 A6 A8 A10 A12 A14 A16 1 0−2.688E−02 8.887E−03 −8.019E−02 1.214E−01 −1.226E−01 6.317E−02−1.233E−02 2 0 −2.989E−02 −1.808E−02 −4.497E−03 2.086E−02 −2.045E−021.337E−02 −3.563E−03 3 0 3.497E−02 −9.953E−03 9.446E−03 1.577E−031.838E−02 −1.625E−02 3.461E−03 4 0 5.312E−02 −8.872E−02 1.023E−01−9.381E−02 5.499E−02 −1.606E−02 1.649E−03 5 0 −1.660E−01 5.095E−02−3.198E−02 3.272E−02 −1.096E−02 1.476E−03 −1.253E−04 6 0 −1.851E−011.117E−01 −7.777E−02 5.380E−02 −1.767E−02 7.232E−04 7.930E−04 7 0−1.576E−02 −3.730E−02 7.054E−02 −8.131E−02 3.932E−02 −9.131E−035.440E−04 8 0 −1.409E−01 1.247E−01 −7.193E−02 8.501E−03 9.786E−03−5.871E−03 1.093E−03 9 0 −2.501E−01 9.351E−02 −4.968E−02 2.133E−02−7.286E−03 1.113E−03 −5.593E−06 10 0 −1.478E−01 2.914E−02 −5.581E−033.404E−04 1.492E−04 −2.688E−05 9.633E−07 11 0 −2.394E−02 6.574E−031.563E−04 8.575E−05 −3.816E−05 3.224E−06 −4.213E−08 12 0 −2.118E−027.842E−03 1.430E−03 6.739E−05 8.190E−06 −1.058E−06 3.557E−08

The values of the respective conditional expressions are as follows:

-   R6r/f=−3.61-   |R4f/R4r|=1.76-   |f3/f2|=0.67-   f3/f=−1.31-   f3/f6=1.02-   f6/f=−1.28-   D34/f=0.16-   D45/f=0.07-   D56/f=0.09-   T5/T6=0.99-   f56/f=−2.83

Accordingly, the imaging lens of Numerical Data Example 4 satisfies theabove-described conditional expressions. The distance on the opticalaxis X from the object-side surface of the first lens L1 to the imageplane IM (air conversion length for the filter 10) is 5.744 mm, anddownsizing of the imaging lens is attained.

FIG. 11 shows a lateral aberration that corresponds to the image heightratio H, and FIG. 12 shows a spherical aberration (mm), astigmatism(mm), and a distortion (%), respectively. As shown in FIGS. 11 and 12,according to the imaging lens of Numerical Data Example 4, theaberrations are also satisfactorily corrected.

Numerical Data Example 5 Basic Lens Data

TABLE 9 f = 5.49 mm Fno = 2.17 ω = 32.6° i r d nd νd [mm] ∞ ∞ L1  1*2.287 0.519 1.5348 55.7 f1 = 4.637  2*(ST) 27.158 0.038 L2  3* 8.6320.779 1.5348 55.7 f2 = 17.539  4* 104.900 0.046 L3  5* 11.690 0.2471.6503 21.5 f3 = −7.508  6* 3.415 0.642 (=D34) L4  7* −7.379 0.5421.6142 25.6 f4 = −63.845  8* −9.343 0.503 (=D45) L5  9* 2.000 0.4811.5348 55.7 f5 = 11.565 10* 2.708 0.941 (=D56) L6 11* −2.855 0.4141.5348 55.7 f6 = −6.698 12* −14.763 0.100 13 ∞ 0.210 1.5168 64.2 14 ∞0.544 (IM) ∞

-   f56=−25.637 mm-   T5=0.481 mm-   T6=0.414 mm

TABLE 10 Aspherical surface data i k A4 A6 A8 A10 A12 A14 A16 1 0−2.793E−02 7.178E−04 −8.124E−02 1.294E−01 −1.213E−01 5.877E−02−1.138E−02 2 0 −4.139E−02 3.907E−03 −2.790E−02 5.134E−02 −5.109E−022.425E−02 −4.553E−03 3 0 1.045E−02 3.201E−02 −2.796E−02 5.620E−02−5.726E−02 2.699E−02 −5.298E−03 4 0 7.741E−03 −5.130E−02 1.086E−01−1.286E−01 7.041E−02 −2.013E−02 2.451E−03 5 0 −1.031E−01 4.931E−02−2.892E−02 2.893E−02 −1.453E−02 4.166E−03 −7.346E−04 6 0 −8.813E−027.940E−02 −5.528E−02 1.216E−03 6.403E−02 −5.382E−02 1.518E−02 7 0−5.052E−02 −1.158E−02 2.845E−02 −6.309E−02 4.081E−02 −1.279E−022.917E−04 8 0 −1.237E−01 8.648E−02 −4.983E−02 5.278E−03 9.637E−03−5.935E−03 1.153E−03 9 0 −2.241E−01 8.108E−02 −4.820E−02 2.106E−02−5.895E−03 7.952E−04 −3.267E−05 10 0 −1.472E−01 2.706E−02 −5.371E−034.066E−04 1.575E−04 −2.967E−05 8.922E−07 11 0 −3.244E−02 5.627E−035.941E−04 −2.230E−06 −2.509E−05 2.290E−06 −2.102E−08 12 0 −3.044E−029.192E−03 −1.559E−03 5.812E−05 9.549E−06 −1.041E−06 3.161E−08

The values of the respective conditional expressions are as follows:

-   R6r/f=−2.69-   |R4f/R4r|=0.79-   |f3/f2|=0.43-   f3/f=−1.37-   f3/f6=1.12-   f6/f=−1.22-   D34/f=0.12-   D45/f=0.09-   D56/f=0.17-   T5/T6=1.16-   f56/f=−4.67

Accordingly, the imaging lens of Numerical Data Example 5 satisfies theabove-described conditional expressions. The distance on the opticalaxis X from the object-side surface of the first lens L1 to the imageplane IM (air conversion length for the filter 10) is 5.934 mm, anddownsizing of the imaging lens is attained.

FIG. 14 shows a lateral aberration that corresponds to the image heightratio H, and FIG. 15 shows a spherical aberration (mm), astigmatism(mm), and a distortion (%), respectively. As shown in FIGS. 14 and 15,according to the imaging lens of Numerical Data Example 5, theaberrations are also satisfactorily corrected.

Numerical Data Example 6 Basic Lens Data

TABLE 11 f = 5.08 mm Fno = 1.99 ω = 34.6° i r d nd νd [mm] ∞ ∞ L1  1*2.209 0.542 1.5348 55.7 f1 = 4.001  2*(ST) −62.450 0.187 L2  3* −7.0100.689 1.5348 55.7 f2 = 9.472  4* −3.041 0.030 L3  5* 10.459 0.274 1.650321.5 f3 = −5.822  6* 2.751 0.607 (=D34) L4  7* −4.332 0.512 1.6142 25.6f4 = 17.675  8* −3.235 0.369 (=D45) L5  9* 3.293 0.698 1.5348 55.7 f5 =−34.703 10* 2.590 0.506 (=D56) L6 11* −2.963 0.539 1.5348 55.7 f6 =−7.457 12* −12.256 0.100 13 ∞ 0.210 1.6168 64.2 14 ∞ 0.544 (IM) ∞

-   f56=−6.471 mm-   T5=0.698 mm-   T6=0.539 mm

TABLE 12 Aspherical surface data i k A4 A6 A8 A10 A12 A14 A16 1 0−2.596E−02 2.757E−03 −7.329E−02 1.144E−01 −1.207E−01 6.250E−02−1.210E−02 2 0 −2.507E−02 −1.746E−02 −8.533E−03 2.027E−02 −1.992E−021.208E−02 −3.009E−03 3 0 4.373E−02 −9.242E−03 1.118E−02 2.401E−041.740E−02 −1.554E−02 3.395E−03 4 0 5.239E−02 −8.086E−02 9.592E−02−8.975E−02 5.428E−02 −1.737E−02 2.179E−03 5 0 −1.763E−01 4.782E−02−3.744E−02 3.990E−02 −1.545E−02 3.732E−03 −6.114E−04 6 0 −1.802E−019.505E−02 −5.914E−02 2.331E−02 4.798E−03 −7.399E−03 2.062E−03 7 03.553E−02 −6.708E−02 9.821E−02 −1.189E−01 6.506E−02 −1.899E−02 1.520E−038 0 −6.748E−02 7.804E−02 −4.361E−02 3.026E−03 7.772E−03 −5.511E−031.306E−03 9 0 −2.259E−01 1.122E−01 −7.908E−02 4.740E−02 −1.918E−023.802E−03 −2.417E−04 10 0 −1.436E−01 3.085E−02 −6.254E−03 3.463E−041.686E−04 −2.837E−05 9.943E−07 11 0 −1.051E−02 −3.019E−03 1.839E−031.404E−05 −4.169E−05 3.352E−06 −5.474E−08 12 0 −2.600E−02 9.413E−03−1.578E−03 6.033E−05 9.496E−06 −1.076E−06 3.288E−08

The values of the respective conditional expressions are as follows:

-   R6r/f=−2.41-   |R4f/R4r|=1.34-   |f3/f2|=0.61-   f3/f=−1.15-   f3/f6=0.78-   f6/f=−1.47-   D34/f=0.12-   D45/f=0.07-   D56/f=0.10-   T5/T6=1.29-   f56/f=−1.27

Accordingly, the imaging lens of Numerical Data Example 6 satisfies theabove-described conditional expressions. The distance on the opticalaxis X from the object-side surface of the first lens L1 to the imageplane IM (air conversion length for the filter 10) is 5.735 mm, anddownsizing of the imaging lens is attained.

FIG. 17 shows a lateral aberration that corresponds to the image heightratio H, and FIG. 18 shows a spherical aberration (mm), astigmatism(mm), and a distortion (%), respectively. As shown in FIGS. 17 and 18,according to the imaging lens of Numerical Data Example 6, theaberrations are also satisfactorily corrected.

Numerical Data Example 7 Basic Lens Data

TABLE 13 f = 5.10 mm Fno = 1.99 ω = 34.5° i r d nd νd [mm] ∞ ∞ L1  1*2.125 0.534 1.5348 55.7 f1 = 4.132  2*(ST) 50.377 0.198 L2  3* −8.4180.641 1.5348 55.7 f2 = 8.159  4* −2.950 0.030 L3  5* 16.499 0.273 1.650321.5 f3 = −5.651  6* 2.986 0.552 (=D34) L4  7* −3.574 0.477 1.6142 25.6f4 = 12.047  8* −2.532 0.273 (=D45) L5  9* −29.841 0.775 1.5348 55.7 f5= −228.717 10* −39.827 0.804 (=D56) L6 11* −2.553 0.394 1.5348 55.7 f6 =−5.242 12* −30.151 0.100 13 ∞ 0.210 1.5168 64.2 14 ∞ 0.545 (IM) ∞

-   f56=−5.063 mm-   T5=0.775 mm-   T6=0.394 mm

TABLE 14 Aspherical surface data i k A4 A6 A8 A10 A12 A14 A16 1 0−2.256E−02 1.101E−02 −8.904E−02 1.367E−01 −1.362E−01 6.745E−02−1.282E−02 2 0 −2.096E−02 −1.863E−02 −7.421E−03 2.117E−02 −2.215E−021.385E−02 −3.585E−03 3 0 3.715E−02 −5.004E−03 6.698E−03 −1.751E−022.257E−02 −1.857E−02 3.900E−03 4 0 4.774E−02 −7.266E−02 9.292E−02−9.145E−02 5.784E−02 −1.890E−02 2.306E−03 5 0 −1.724E−01 4.875E−02−2.364E−02 2.381E−02 −8.693E−03 3.145E−03 −8.407E−04 6 0 −1.748E−019.749E−02 −6.128E−02 2.437E−02 4.100E−03 −6.963E−03 1.967E−03 7 03.289E−02 −5.090E−02 8.599E−02 −1.176E−01 6.456E−02 −1.768E−02 1.431E−038 0 −4.464E−02 7.835E−02 −4.262E−02 8.000E−04 7.613E−03 −5.454E−031.565E−03 9 0 −1.865E−01 1.368E−01 −1.069E−01 6.038E−02 −2.243E−023.539E−03 3.101E−05 10 0 −1.051E−01 3.022E−02 −5.853E−03 4.123E−041.710E−04 −3.185E−05 7.277E−07 11 0 −5.623E−02 1.462E−02 1.978E−044.776E−06 −7.447E−06 1.126E−05 −3.647E−07 12 0 −2.865E−02 7.320E−03−1.266E−03 6.345E−05 8.429E−06 −1.209E−06 3.517E−08

The values of the respective conditional expressions are as follows:

-   R6r/f=−5.91-   |R4f/R4r|=1.41-   |f3/f2|=0.69-   f3/f=−1.11-   f3/f6=1.08-   f6/f=−1.03-   D34/f=0.11-   D45/f=0.05-   D56/f=0.16-   T5/T6=1.97-   f56/f=−0.99

Accordingly, the imaging lens of Numerical Data Example 7 satisfies theabove-described conditional expressions. The distance on the opticalaxis X from the object-side surface of the first lens L1 to the imageplane IM (air conversion length for the filter 10) is 5.734 mm, anddownsizing of the imaging lens is attained.

FIG. 20 shows a lateral aberration that corresponds to the image heightratio H, and FIG. 21 shows a spherical aberration (mm), astigmatism(mm), and a distortion (%), respectively. As shown in FIGS. 20 and 21,according to the imaging lens of Numerical Data Example 7, theaberrations are also satisfactorily corrected.

As described above, according to the imaging lens of the embodimentdescribed above, it is achievable to have very wide angle of view (2w)of 60° or greater. More specifically, according to Numerical DataExamples 1 to 7, the imaging lenses have wide angles of view of 65.2° to70.0° . According to the imaging lens of the embodiment, it is possibleto take an image over a wider range than that taken by a conventionalimaging lens.

Moreover, in these years, with advancement in digital zoom technology,which enables to enlarge any area of an image obtained through animaging lens by image processing, an imaging element having a high pixelcount is often used in combination with a high-resolution imaging lens.In case of such an imaging element with a high pixel count, alight-receiving area of each pixel often decreases, so that an imagetends to be dark. According to the imaging lenses of Numerical DataExamples 1 to 7, the Fnos are as small as 1.97 to 2.18. According to theimaging lens of the embodiment, it is achievable to obtain asufficiently bright image, even when the imaging lens is applied incombination with the high-pixel imaging element described above.

Accordingly, when the imaging lens of the embodiment is mounted in animaging optical system, such as cameras built in portable devicesincluding cellular phones, smartphones, and portable informationterminals, digital still cameras, security cameras, vehicle onboardcameras, and network cameras, it is possible to attain both highperformance and downsizing of the cameras.

The present invention is applicable to an imaging lens to be mounted inrelatively small cameras, such as cameras to be built in portabledevices including cellular phones, smartphones, and portable informationterminals, digital still cameras, security cameras, vehicle onboardcameras, and network cameras.

The disclosure of Japanese Patent Application No. 2016-096676, filed on05/13/2016, is incorporated in the application by reference.

While the present invention has been explained with reference to thespecific embodiment of the present invention, the explanation isillustrative and the present invention is limited only by the appendedclaims.

What is claimed is:
 1. An imaging lens comprising: a first lens havingpositive refractive power; a second lens having positive refractivepower; a third lens; a fourth lens; a fifth lens; and a sixth lenshaving negative refractive power, arranged in this order from an objectside to an image plane side, wherein said sixth lens is formed in ashape so that a curvature radius of a surface thereof on the object sideand a curvature radius of a surface thereof on the image plane side arenegative, and said sixth lens has the surface on the image plane sidehaving the curvature radius R6r so that the following conditionalexpression is satisfied:−10<R6r/f<−1, where f is a focal length of a whole lens system.
 2. Theimaging lens according to claim 1, wherein said fourth lens is formed ina shape so that a surface thereof on the object side has a curvatureradius R4f and a surface thereof on the image plane side has a curvatureradius R4r so that the following conditional expression is satisfied:0.5<|R4f/R4r|<2.0.
 3. The imaging lens according to claim 1, whereinsaid second lens has a focal length f2 and said third lens has a focallength f3 so that the following conditional expression is satisfied:0.2<|f3/f2|<1.2.
 4. The imaging lens according to claim 1, wherein saidthird lens has a focal length f3 so that the following conditionalexpression is satisfied:−2.0<f3/f<−0.5.
 5. The imaging lens according to claim 1, wherein saidthird lens has a focal length f3 and said sixth lens has a focal lengthf6 so that the following conditional expression is satisfied:0.5<f3/f6<1.5.
 6. The imaging lens according to claim 1, wherein saidsixth lens has a focal length f6 so that the following conditionalexpression is satisfied:−2.0<f6/f<−0.5.
 7. The imaging lens according to claim 1, wherein saidthird lens is arranged to be away from the fourth lens by a distance D34on an optical axis thereof so that the following conditional expressionis satisfied:0.05<D34/f<0.2.
 8. The imaging lens according to claim 1, wherein saidfourth lens is arranged to be away from the fifth lens by a distance D45on an optical axis thereof so that the following conditional expressionis satisfied:0.02<D45/f<0.2.
 9. The imaging lens according to claim 1, wherein saidfifth lens is arranged to be away from the sixth lens by a distance D56on an optical axis thereof so that the following conditional expressionis satisfied:0.05<D56/f<0.2.
 10. The imaging lens according to claim 1, wherein saidfifth lens has a thickness T5 along an optical axis thereof and saidsixth lens has a thickness T6 along an optical axis thereof so that thefollowing conditional expression is satisfied:0.5<T5/T6<3.0.
 11. The imaging lens according to claim 1, wherein saidfifth lens and said sixth lens have a composite focal length f56 so thatthe following conditional expression is satisfied:−10<f56/f<−0.5.
 12. The imaging lens according to claim 1, wherein saidfirst lens has Abbe's number vd1, said second lens has Abbe's numbervd2, and said third lens has Abbe's number vd3, so that the followingconditional expressions are satisfied:35<vd1<75,35<vd2<75,15<vd3<35.
 13. The imaging lens according to claim 1, wherein saidfourth lens has Abbe's number vd4, said fifth lens has Abbe's numbervd5, and said sixth lens has Abbe's number vd6, so that the followingconditional expressions are satisfied:15<vd4<35,35<vd5<75,35<vd6<75.
 14. The imaging lens according to claim 1, wherein said sixthlens has the surface on the image plane side formed in an aspheric shapeso that a curvature thereof increases monotonously away from an opticalaxis thereof toward a periphery thereof in a direction perpendicular tothe optical axis.